There are various types of valves for hydraulically striking devices on the market. Similar for many of these hydraulically striking devices may be that there is a piston that hydraulically reciprocates between a first position and a second position and that movement is controlled hydraulically with a controlling arrangement which is in connection with the device, which controlling arrangement may be a valve for example inside the device. This valve comprises a moving member or a similar type of device that moves back and forth inside the housing of the valve. The moving member controls the fluid flow that is needed for moving the piston. The valve is operated by means of hydraulic pressure.
Hydraulically striking devices are used in the hydraulic machines that are, for example, working in rock drilling or similar applications. Rock drilling is usually performed in mines and construction plants. In some of the mining plants it is not uncommon that they can produce hundreds of thousands of tons of ore from the rock in a year. The hydraulically striking device is also used for drilling and sampling, general excavations, tunneling work and roof bolting. On the work site, the hydraulically striking device can be used for drilling of rock. One example of test results of one rock drilling equipment working on the drilling site shows typical operating values of the machine equipped with one model-size hydraulically striking device such as a penetration rate of around 2 meters/minute in granite with a drill hole diameter of around 50 mm when using a percussion pressure from around 100 bar up to 200-300 bar. On the drill site, around or over 100 mm holes are not uncommon for the rock drilling equipment.
Usually, a valve is provided inside the hydraulically striking device and is designed to last in the hard working environment of the machine. The valve is usually larger than a standard-size screw-in cartridge valve, robust and strongly built, as the hydraulically striking device can strike generally from 30 to 100 times in a second. The hydraulically striking device can weigh up to hundreds of kilos. But in the future, bigger and heavier models are needed when the demands from the industry rise. Also, demands for a higher striking force with lower flows raise the demands for the equipment so that the operating pressures of the hydraulically striking device can be at a higher-than-normal level.
But in many of these valves, a common problem is that a sticking effect is created in the moving member when pressure of the hydraulic fluid is conducted inside the valve. The surface that is towards the moving member is seldom even, which causes leakage and changes the pressure on that side. The pressure difference between opposite ends of the moving member creates an unwanted force acting towards the end that is at the lower pressure.
This unwanted force can create the mentioned sticking effect. The force can be diminished by diminishing the area of the sealing surface.
On the other side of the moving member, an opposite situation occurs. Pressure from the pressure line leaks inside the valve and creates a force opening the moving member, which creates more leakage. At first, this leakage is created because of the uneven surface of the sealing surface.
A common way to eliminate this sticking effect and leakage is to manufacture the end of the moving member substantially sharp. But this sharp edge is a problem in the hydraulically striking device because the moving member beats rapidly itself towards the housing of the valve, and this sharp edge does not last when the valve is used and in time will be worn off. This type of a sharp edge will create metal chips into the hydraulic fluid when it is used, and metal chips can create malfunction in a hydraulic system for example by jamming the movement of moving parts inside the device.
The objective of the invention is to eliminate or at least alleviate the problems mentioned above and introduce solutions for them.